Method of using a minimum cost EVPV for vehicle-solar-grid integration

ABSTRACT

This invention consists of an apparatus to interface an electric vehicle battery with a solar photovoltaic system and a method of using the apparatus to provide back up power during grid outages and ancillary service revenue from the grid. The apparatus uses the solar PV inverter to provide bidirectional power flow from the battery during night-time hours, or whenever the solar array is producing insufficient power. The apparatus thus consists only of switches and control and measurement equipment. It relies on the otherwise underutilized inverter and the on-board vehicle battery charger as the power electronic components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application“Vehicle-Solar-Grid Integration” Ser. No. 14/101,423 filed Dec. 10,2013, now published as US-2015-0162784-A1, by the present inventor, andProvisional Patent Applications “Bidirectional Power ElectronicInterface” No. 61/889,067, filed Oct. 10, 2013, “Bidirectional PowerElectronic Interface with Sustaining Power” 61/921,583, filed Dec. 30,2013, “Vehicle-Solar-Grid Integration with Supplementary Battery”62/050,819, filed Sep. 16, 2014, and “Low-Cost EVPV forVehicle-Solar-Grid Integration”, filed Feb. 19, 2016, by the presentinventor.

This application claims priority dating to Provisional PatentApplication No. 62/299,756 entitled “Minimum Cost EVPV forVehicle-Solar-Grid Integration” filed on Feb. 25, 2016.

FEDERALLY SPONSORED RESEARCH

None

CITED LITERATURE

SAE J-1772 revised October 2012, p 32.

IEEE Standard 1547 net metering interconnection to the grid

BACKGROUND OF THE INVENTION

Electric vehicles with large storage batteries represent anunderutilized resource that can serve to stabilize the electric utilitygrid and reduce the requirement for additional investment indistribution and transmission equipment, if they can be remotelydirected to take or provide AC power. The communication technology forthe remote control exists, together with an existing market forancillary services to the grid. Solar inverters can convert DC powerfrom the battery to AC power for the grid.

This bidirectional flow of power can provide valuable services to theutility grid. An example of the latter is frequency regulation in whichbattery storage can take excess power or provide needed power instantlyon request from the Independent System Organization or RegionalTransmission Organization (ISO/RTO) responsible for grid stability. TheISO/RTOs pay for this ancillary service in a daily auction market.Another service is demand response in which the battery can stopcharging at periods of peak demand when the power is needed elsewhere onthe grid. This service is also recompensed by the RTO/ISO.

For commercial and industrial vehicle owners, the vehicle battery canprovide power to offset peak demand during the daytime and thus reducethe monthly demand charge imposed by the local distribution company.There is an opportunity for energy arbitrage in which the vehicle ischarged at night when prices are low and partially discharged during theday if the value of the power is greater than its value in propellingthe vehicle.

This invention utilizes the photovoltaic inverter of an existing solarphotovoltaic system, and the on-board charger provided with the vehicleto provide a minimum-cost, bidirectional Electric Vehicle PhotoVoltaic(EVPV) interface. This interface can be programmed to maintain thevehicle in a suitable state of charge to provide the driving rangeneeded by the owner using power from the grid at the optimum time tominimize cost, and to provide ancillary services to the grid to generaterevenue to offset the cost of the vehicle and its energy supply.

The availability of AC power flow from the battery also provides a backup power supply to the vehicle owner when there are grid outages tomaintain essential services such as heating and water pumps. Thiscapability is particularly valuable in conjunction with a solarphotovoltaic array which can provide power to keep the battery and thevehicle charged during outages and which in turn can be kept operatingby “islanding” from the grid rather than shutting down as required byIEEE standard 1547 to avoid putting power back on the grid during anoutage.

For both ancillary service and owner service it is an advantage to havethe battery connected at all times to maximize revenue and convenience.However, by the nature of a vehicle, the vehicle battery is going to bedisconnected when the vehicle is in use. This may be for as little as anhour or two or as much as 8 or 10 hours per day depending on use of thevehicle. An auxiliary stationary battery may be provided to maintaincontinuity of service while the vehicle is in use.

BRIEF SUMMARY OF THE INVENTION

This invention comprises the method of interfacing a large battery pack,as in an electric vehicle, with a grid-tied inverter in a photovoltaicsystem to provide ancillary services to the electric utility grid, andback up emergency power during grid outages, and the apparatus toaccomplish the integration. The apparatus is an Electric VehiclePhotoVoltaic (EVPV) integrator. In a previous patent application(2015-0162784) a similar apparatus comprising an off-board batterycharger and a DC-DC converter of substantially equal capacity, withswitching and control equipment to interface with the electric utilitygrid ISO, and appropriate cords and connectors to interface with thevehicle or other battery pack was described. The present inventionaccomplishes the same objective by using the on-board charger that issupplied by the vehicle and direct connecting the vehicle battery to anexisting Photovoltaic inverter to reduce the cost of the EVPV. The EVPVconsist only of switches and controls and communication means toaccomplish the various functions enabled by the bidirectional connectionto the vehicle battery.

BRIEF DESCRIPTION OF THE DRAWINGS

The means by which this objective is achieved by the present inventionis illustrated in the accompanying Figures:

FIG. 1 is a schematic drawing of the apparatus of this invention in atypical installation illustrating the method of operation.

FIG. 2 is a schematic drawing of the apparatus of this invention with anauxiliary fixed battery hard-wired into the apparatus, or into which theapparatus can be plugged to maintain ancillary services and emergencypower when the vehicle is in use.

DETAILED DESCRIPTION OF THE INVENTION The Preferred Embodiment

In FIG. 1 EVPV of this invention 20, is shown interfaced with AC wiringin building 30. An electric vehicle is supplied with AC power from EVPV20 and Electric Vehicle Service Equipment 24 through connection 16 whichmay be the standard SAE J1772 level 2 plug and receptacle. The EVPV isalso connected direct to the vehicle battery pack through DC connection18, which may be any of the standard DC quick charge standards such athe Japanese standard CHAdeMO connector or the SAE CCS Combo connectorused in German and US made vehicles. The CCS is convenient because itcan connect both the AC and DC circuits through a single plug andreceptacle. Tesla vehicles accomplish the same objective through theJ-1772 connector by switching between AC regular and DC fast chargingmodes depending on signals relayed from the charger specifying itsnature. There is an SAE J-1772 AC Level 2, DC Level 1 standard for thistype of single connection, dual mode charging also. EVPV 20 is connectedto the building 30 power installation by permanent AC and DC wiring.

EVPV 20 is hard wired to PV inverter 32 via switch 42. During thedaylight hours when PV array 34 is producing power switch 42 is in thedaytime position shown providing DC power to inverter 32 which convertsit to AC power. The AC power flows through solar power meter 36 tocritical load panel 38 and automatic transfer switch 80 to main loadpanel 39. Any excess power flows to the grid via net meter 40. There isa branch circuit from critical load panel 38 providing EVPV 20 with ACpower to supply Electric Vehicle Service Equipment (EVSE) 24 whichconnects through connector 16 with the battery charger on board thevehicle.

At night when the PV array is no longer producing power switch 42connects the inverter 32 to the vehicle battery to convert battery DCpower to AC power. Vehicle battery packs are typically supplied at anominal voltage of 300 to 400 VDC. Typical solar installations operateat 300 to 600 V, and even higher. Thus there is a good match between thevoltage levels of low-cost, high-powered PV inverters and vehiclebattery packs. This bidirectional connection to the vehicle batterythrough inverter 32 and EVSE 24 allows for the EVPV to provide ancillaryservices to the grid such as frequency regulation. These services areprovided under Demand Response regulations which prohibit “injection” ofpower onto the grid even from net-metered solar installations. Thepresent invention provides for net-metered solar production during thedaylight hours and non-injecting ancillary service provision at nightusing the same components for maximum utilization and return oninvestment in the solar-electric vehicle combination.

The EVPV also contains control and switching equipment to accomplish thedesired ancillary service functions. These functions are controlled byup regulation control means 23 and down regulation control means 25.These regulation control means are in turn interfaced to grid RTO/ISOancillary service requests via Data Acquisition and Control System(DACS) 26 and Ethernet switch 58. DACS 26 may also control switch 27 topermit charging the battery pack only at times of favorable electricityprices to achieve TOU charging and to interrupt charging during periodsof high demand to achieve demand management. Data on the response of thesystem from current transformers 54 and 56 are fed through switch 58 tothe RTO/ISO via the internet.

In operation switches 23, 25 and 27 are controlled by site DACScontroller 26, a locally-sited micro computer with communication via theinternet or otherwise to frequency regulation and demand responsesignals from the local RTO/ISO which are managed by an off siteaggregator. The aggregator combines individual vehicles to provide aminimum capability of use to the ISO in maintaining grid stability,typically 0.1 to 1.0 megawatts, (10 to 150 vehicles). The provision ofancillary service requires that the power consumed or fed to the grid beproportional to the need transmitted by the ISO. This can be achieved byusing proportionate controls on the inverter 32 and EVSE 24 as enabledby the J-1772 protocol for electric vehicle charging. Alternatively thecharger and inverter may be controlled by simple on/off switches and thepower of the aggregate controlled by the aggregator to provide aproportional output determined by how many of the vehicles are switchedon at any time. A high impedance bypass connection 55 around switch 23may be required to keep the inverter synchronized when control means 23is off. Data flows from the EVPV through the aggregator to the ISOconfirming performance and payments flow from the ISO to the aggregatorand on to the vehicle owner or financial beneficiary.

Site controller 26 also receives requests from the vehicle operator asto the required state of charge needed to fulfill the expected missionof the vehicle and provides data on the current status.

In addition to providing demand response service to the utility grid,the flow of power from EVPV 20 to building 30 can be controlled by sitecontroller 26 to offset peak demands for power and thus reduce thedemand charge on the owner's monthly utility bill. This charge typicallyamounts to $10 to $20 per kW measured in any 15 minute period in themonth and the peak demand charge is typically billed for 6 months to ayear after it is incurred. There is thus a substantial incentive toreduce demand which inverter 20 can do, provided that it has access tobattery storage.

Other Embodiments

Back-Up Power Supply

The bidirectional connection of this invention also can provide back uppower in emergencies when the grid fails. It does this in an optimum wayby maintaining operation of the solar PV installation during the outage.Solar PV inverters contain “anti-islanding” features and are IEEE 1547compliant for connection to the grid. This means that in an outage thePV system shuts down to avoid feeding power back onto the grid andendangering linemen attempting to fix the problem. In this inventionautomatic transfer switch 80 opens during an outage to “island” thebuilding from the grid. Uninteruptable power supply 37 maintains powerto keep inverter 32 functioning to provide power to critical loads 38and EVSE 24. During the night-time hours when the PV array is notproducing the vehicle battery can provide power via inverter 32 tosupport the critical loads during the outage. Switch 80 will need anintermediate off position in reconnecting to the grid on restoration ofgrid power to allow inverter 32 to unsynchronize from microgrid 20 andresynchronize with the grid per IEEE1547.

Supplementary Fixed Battery

In FIG. 2 a supplementary battery 82 with charger 84 and receptacles 86and 88 may be provided to keep inverter 32 functioning while the vehicleis unplugged and operating. This may be most easily accomplished byunplugging the inverter from the vehicle and plugging it into thesupplementary battery.

Alternatively, as shown in FIG. 2, supplemental battery 82 may be hardwired in parallel with vehicle connections 16 and 18. In this case avery close match between the vehicle batteries and fixed battery 82 isnecessary since they are connected in parallel by the DC links 18 and88. The use of vehicle batteries that have lost some of their capacityfor stationary provision of ancillary services has been discussed in theliterature and would be ideal in this application. A hard-wiredconnection to battery 82 will provide a fast charge up to approximately50% State Of Charge to the vehicle when the latter is completelydischarged at hook up.

Provision of supplemental battery 82 means that EVPV 20 is available 24hours per day regardless of the vehicle usage. It supports ancillaryservices, demand charge management and emergency power during prolongedoutages allowing the vehicle to be used while the building is stillpowered.

The invention claimed is:
 1. A method comprising the steps of:installing an Electric Vehicle Photovoltaic (EVPV) apparatus in relationto a building, which apparatus is equipped with a photovoltaic powersystem including an inverter to invert DC electric energy produced byphotovoltaic panels into AC electric energy compatible with an electricgrid which supplies electric energy to the building, a Data Acquisitionand Control System (DACS) to control the operation of the EVPVapparatus, and an automatic or manual transfer switch in the building,which can isolate the building and the EVPV apparatus from the electricgrid in the event of a power failure, attaching the apparatus to anelectric vehicle by an AC connection to recharge a vehicle battery whichstores electric energy to drive the vehicle through an on-board vehiclecharger supplied with the vehicle, and simultaneously attaching theapparatus to the electric vehicle battery by a DC connection through aDC quick charge port of the vehicle, which can take electric energy fromthe vehicle battery to supply the photovoltaic inverter of the PVsystem, and, under control of the DACS, either taking AC electric energyfrom the grid to recharge the vehicle battery through the AC connection,or taking DC electric energy from the vehicle battery through the DCconnection to provide AC output from the PV system inverter to thebuilding for use during power failures when the supply from the grid isunavailable, and for other uses.
 2. The method of claim 1 in which theEVPV apparatus is also used to provide ancillary services to a RegionalTransmission Operator/Independent System Operator (RTO/ISO), whichcontrols the operation of the grid supplying electric energy to thebuilding and communicates with the DACS through an aggregator, byproviding power to the grid from the Electric Vehicle battery throughthe DC connection and the photovoltaic inverter in response to frequencyregulation requests from the RTO/ISO for an increase in electric powergeneration, or taking power from the grid through the AC connection torecharge the battery in response to frequency regulation requests for adecrease in power generation, and responding to Demand Response requestsfrom the RTO/ISO to curtail demand.
 3. The method of claim 1 in whichthe EVPV apparatus is also used for energy arbitrage to take electricenergy from the grid at times of low demand and low cost to recharge thevehicle battery, and to provide electric energy to the building from thevehicle battery at times of high demand and high cost to lower theaverage cost of electric energy to supply the building and to reducedemand charges for electric power demand by the building.
 4. The methodof claim 1 in which the EVPV apparatus is used to maintain the operationof the Photovoltaic Power system during power failures by addition of anuninterruptible power supply to maintain an AC voltage on the output ofthe inverter, allowing it to continue to provide energy to supplementthe vehicle battery and the DC connection to serve critical loads andrecharge the electric vehicle.